During horizontal drilling with a percussion implement, a hammer provided in the percussion implement is accelerated, for example with a source of pressure medium, such as water, air or other media. The kinetic energy of the hammer is directed without retardation into the drill head during the driving of the drilling implement. For the propulsion, the mass of the entire drilling implement located in the earth, including the pressure-medium hose, is to be accelerated. Furthermore, the skin friction of the drilling implement with the surrounding earth is to be overcome and displacement work is to be performed in the region of the drill head. All this is performed by the percussion piston.
Difficulties during the driving with such a percussion implement occur in particular in stony or rocky soils, in which the percussion energy partly applied by the skin friction and by the drilling implement mass to be moved is not sufficient in order to direct the shattering energy, required for overcoming an obstacle, into the obstacle, such as, for example, a stone or a piece of rock. This problem has been solved for quite some time by a special configuration of the driving heads (“stepped head”), as described in DE 25 58 842.5 A1.
The percussion energy can thus be directed into the obstacle as concentrically as possible by means of a stepped drill head in order to achieve the requisite shattering energy without the occurrence of substantial disadvantages with the displacement properties of the drill head.
DE 21 57 259 A1 and DE 26 34 066 A1 disclose a driving head which, movable in the axial direction, is connected to the percussion implement. As a result, uncoupling of the forward movement of driving head and percussion implement is achieved, which leads to the entire percussion energy of the percussion piston being available in a first step in the driving head for displacement work and for shattering obstacles. It is not until the obstacle at the face has been overcome, that is to say the path for the driving head is free, that the driving energy of the percussion piston is directed via the driving head no longer solely into the face, but rather a large proportion of said driving energy is directed via the connection between driving head and housing of the percussion implement into the percussion implement, so that the latter is drawn up.
Such a driving head has proved successful in practice and has been used for many years in horizontal percussion driving. However, depending on the dimensioning of the percussion implement or intractability of the obstacle to be overcome, there are practical limits, at given percussion energy, to the use of the driving head described.